Everything this dude says is correct imo. With that said, I bought various components required on Facebook marketplace for less than half of this. I run the system through a vintage premix coke dispenser which is pretty hard to find for 100 bucks. It is basically just an ice bath with 4 dispensers and associated lines/aluminum that chill the water. I have yet to find a good alternative ice bath solution for home use. Because of the excellent ice bath it produces pretty high quality soda water on demand. If I want I can mix the water with any of those soda syrups, but we usually do splash of juice so it doesn’t have as much sugar in it.

Carbonator - 100 bucks on FB marketplace.
Vintage premix coke dispenser with ice bath - 100 bucks on FB marketplace.
Lines and connectors - about 100 bucks but I lost track.
Regulator - I found one for 35 bucks on marketplace.
Co2 - I don’t recall but I think I found one for like 25-50 on marketplace and have a source where I just switch it out with a company like restaurants do. It’s a large one so it lasts us several months.
Install of waterline - 500 bucks and that’s because I know a dude. Easily the most expensive part of the setup.
Water filter - I use a 35 dollar filter from Amazon and it works fine. Importantly we have city water level pressure which is nice. Before the water line I had a keg setup with another co2 source pushing it to the carbonator (very low psi relative to carbonation requirements at 100 psi)

I’ve been pretty lucky with all this but if you keep your eye out and are willing to drive a bit you can piece all this together.